The present invention relates to welding of lap-penetration joints, more particularly to gas metal buried arc welding of lap-penetration joints.
Gas metal arc (GMA) welding of metal components involves application of current to a consumable metal electrode in a torch and forming an arc between the tip of the electrode and a surface of the components. The metal of the electrode deposits as a filler material onto the components, and a molten pool of metal forms that includes a mixture of the metals of the electrode and of the component. A weld joint forms upon solidification of the molten metal. GMA welding is generally used for joining relatively thin (1 mm-4.5 mm) components in arrangements such as lap-fillet, tee-fillet and square butt joints. FIG. 1 is a schematic of GMA welding of a square butt joint between two components 2, 4 in which an arc 6 is produced from a metal electrode 8. A pool of molten metal 10 forms between the electrode 8 and components 2, 4 to produce a weld bead 12 which solidifies behind the moving weld region of the arc 6 and molten pool 10. These joints (lap-fillet, tee-fillet and square butt) require that the tip 14 of the electrode and the arc are laterally placed within xc2x10.5 mm of the joint edge being welded. While use of robotics and fixturing provides control over the welding operation, several techniques have been used to ensure that the lateral placement of the electrode arc is correct relative to the joint.
One solution is to use dimensionally accurate components and welding fixtures, which adds significant costs to the final cost of the process. Alternatively or in addition, the torch and arc may be oscillated relative to the joint edges to compensate for variations in the edges or the edge locations due to variations in dimensional tolerances of parts, welding fixtures and/or positioners as well as variations in the lateral placement of the electrode tip and arc relative to the joints. While torch oscillation overcomes greater variability in the joint edges, a major drawback is a significant reduction in productivity, i.e. the welding speed of travel is reduced to allow for oscillation to occur. Other methods of improving the joint/electrode relationship employ vision based seam-tracking systems, most of which are expensive, unreliable with aluminum components and maintenance intensive. Tactile seam tracking systems are effective, but have limited applicability to welding three-dimensional assemblies such as sharp corners or in accommodating changes in direction or creating several short joints.
Moreover, conventional practice teaches that lap-penetration joints are not suitable for GMA welding because the weld (from the molten metal pool 10) does not reach sufficient depths in the component stack to melt and fuse the lower component with the weld upon solidification, i.e. does not penetrate into the lower component. Although, spot welding of lap-penetration joints with the GMA welding has been known for many years, its uses have been limited to structurally non-critical joints for the several reasons. The combination of short welding time, insufficient current density applied during spot welding and inability to cathodically clean the surface oxides,present on the faying surfaces between the overlapping parts, have resulted in xe2x80x9cwine-cup xe2x80x9d shaped profiles of spot welds with limited weld penetration into the lower component and insufficient interfacial weld width. This makes GMA welded spot welds relatively weak and of limited endurance under fatigue type loading.
Deeper GMA welding, referred to as gas metal buried arc (GMBA) welding, has been accomplished with square butt joints as shown in FIG. 2. The GMBA welding process differs from conventional GMA welding in that (1) the welding current passed through the welding electrode is significantly higher with the GMBA welding process than with conventional GMA welding. This results in higher current densities in the GMBA welding process, which leads to a more penetrating collimated are arc that penetrates deeper into the components 2, 4. However, deep GMBA welding of law penetration joints has not heretofore been accomplished.
The present invention includes a method of making a lap-penetration joint comprising gas metal arc welding a first metal component to an underlying second metal component by forming an arc between a consumable metal electrode and a surface of the first component, depositing metal from the electrode to the first component and producing a pool of molten metal which extends through the first component and into the second component. Upon solidification of the molten pool metal into a weld, the width of the weld at the interface between the two components is at least equal to the thickness of the thinner of the first component and the second component. During welding, the arc is at least partially buried within the thickness of the first component and is moved in the direction of the desired joint location to produce a joint.